Benefits of a closed loop control system for treating diabetic conditions with monitoring glucose levels and adjusting delivery rate of insulin are well known. Such systems, referred to as artificial pancreas, model healthy pancreas which, when functioning normally, produces insulin (by the beta cells (β-cells)) to counteract the rise in glucose levels in the blood stream. As is known, Type-1 diabetes mellitus condition exists when the beta cells in the pancreas either die or are unable to produce sufficient amount of insulin naturally in response to the elevated glucose levels.
Common treatment of Type-1 diabetes is the use of insulin pumps that are programmed to continuously deliver insulin to the body through an infusion set. The use of insulin pumps to treat Type-2 diabetes (where the beta cells in the pancreas do produce insulin, but an inadequate quantity) is also becoming more prevalent. Such insulin delivery devices are preprogrammed with delivery rates such as basal profiles which are tailored to each user, and configured to provide the needed insulin to the user.
In addition, continuous glucose monitoring systems have been developed to provide real time monitoring of fluctuation in glucose levels. One example is the FreeStyle Navigator® Continuous Glucose Monitoring System available from Abbott Diabetes Care Inc., of Alameda, Calif. The use of such glucose monitoring systems provides the user with real time glucose level information. Using the continuous glucose monitoring system, for example, diabetics are able to determine when insulin is needed to lower glucose levels or when additional glucose is needed to raise the level of glucose.
Using a continuous glucose monitoring system in conjunction with an insulin pump can be an effective treatment tool for individuals with Type-1 or severe Type-2 diabetic condition to maintain their blood sugar levels at a physiologically desirable range. However, for the continuous glucose monitoring system to be effective, characteristics of the continuous glucose monitoring system, particularly the continuous glucose sensor of the system, must be evaluated and accurate. Evaluation of characteristics, such as linearity and lag, associated with continuous glucose sensors can impact glucose control errors and previous methods of evaluating such characteristics, such as linearity, can be confounded by lag, noise and apparent nonlinearities due to data distribution.